internal/rosa: panic error for invalid handle

This enables recovery and better error handling for errors originating from external azalea files.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/state.go

@@ -19,6 +19,9 @@ import (
 // ArtifactH is a handle of the unique name of a prepared [pkg.Artifact].
 type ArtifactH unique.Handle[string]
 
+// H is a convenient function for acquiring an [ArtifactH] by name.
+func H(name string) ArtifactH { return ArtifactH(unique.Make(name)) }
+
 // String returns the name of p.
 func (handle ArtifactH) String() string {
 	return unique.Handle[string](handle).Value()
@@ -39,6 +42,14 @@ func (handle *ArtifactH) UnmarshalJSON(data []byte) error {
 	return nil
 }
 
+// A HandleError is panicked when attempting to acquire an [Artifact] via an
+// invalid [ArtifactH] with the Must suite of methods.
+type HandleError ArtifactH
+
+func (e HandleError) Error() string {
+	return "artifact " + strconv.Quote(ArtifactH(e).String()) + " not available"
+}
+
 type (
 	// Stage denotes the infrastructure to compile a [pkg.Artifact] on.
 	Stage uint32
@@ -234,7 +245,7 @@ func (s *S) Get(handle ArtifactH) (meta *Artifact) {
 func (s *S) MustGet(handle ArtifactH) (meta *Artifact) {
 	meta = s.Get(handle)
 	if meta == nil {
-		panic("artifact " + strconv.Quote(handle.String()) + " not available")
+		panic(HandleError(handle))
 	}
 	return
 }
@@ -270,7 +281,7 @@ func (t Toolchain) Load(handle ArtifactH) (pkg.Artifact, string) {
 func (t Toolchain) MustLoad(handle ArtifactH) (pkg.Artifact, string) {
 	a, version := t.Load(handle)
 	if a == nil {
-		panic("artifact " + strconv.Quote(handle.String()) + " not available")
+		panic(HandleError(handle))
 	}
 	return a, version
 }